package Calculation;

import java.util.Scanner;

public class jj {
    public static void main(String[] args) {
        Scanner reader= new Scanner(System.in);
        int n = reader.nextInt();
        double sum=0.0;
        for(int i=2;i<=n;i+=2){
            sum =sum + 1.0/i;
        }
        System.out.printf("%.4f",sum);
    }
}
